1. Field of the Invention
This invention relates to earth boring equipment used in the rotary system of drilling and more particularly to drill string wall contacting tools for deviation control and/or bit stabilization. This invention specifically concerns the surface of stabilizers used as drill string wall contacting elements in the drilling of oil, gas, geothermal and water wells.
2. Description of the Prior Art
It is known in the art to coat the wear or bearing surfaces of stabilizers with a matrix of nickel and silver containing tungsten carbide particles. This method of preparing stabilizer surfaces suffers from the disadvantage that the nickel silver matrix is soft, having a Rockwell Hardness in the range of Rc 10. This characteristic softness causes the matrix to rapidly be worn away, thereby releasing the embedded tungsten carbide particles and impairing the wear resistance of the stabilizer surface.
Another method commonly used to prepare stabilizer surfaces is to drill a plurality of holes in the surface of a substrate having a Rockwell Hardness in the range of Rc 22-32. Round tungsten carbide particles are then pressed into the drill holes to provide an abrasion resistant surface. A disadvantage of this prior art method is that the substrate must be soft enough to be drilled in the first place, and is accordingly too soft to provide superior wear resistance properties. Another disadvantage is the difficulty of replacing the wear surfaces since they must be cut off with a torch, the area built up with a welding rod, turned to size in a lathe redrilled with holes, and carbide pieces pressed into the holes.
Yet another prior art method is shown in U.S. Pat. No. 3,868,235 issued to Held. The Held patent discloses a method for applying hard carbide particles to the surface of a metal substrate by applying a copper free molten matrix material to the substrate, applying a tacky organic adhesive over the matrix, sprinkling the carbide particles on the adhesive and then baking the layered substrate in a non-oxidizing furnace at a temperature below the melting temperature of the substrate, but high enough to melt the matrix and volatize the adhesive. This process provides porosity to the matrix, but suffers the significant drawback of requiring the presence of a furnace to volatize the adhesive and melt the matrix.
Thus, the two primary drawbacks of the processes shown in the prior art are that the abrasive surfaces provided offer inadequate abrasion resistance and/or require unwieldly, time consuming and expensive procedures in replacing the wear resistant surfaces. Time consuming replacement procedures are especially intolerable in oil-field drilling operations where time consuming delays often translate into the loss of many thousands of dollars.